1. Field of the Invention
The present invention relates to an improvement of a thermal development apparatus for exposing to laser beams or the like a photothermographic material using a dry material. More particularly, the invention relates to a thermal development apparatus which can develop dual-sided photosensitive films.
2. Description of the Related Art
An image recording apparatus for recording images for medical use such as a digital radiography system, CT, or MR (Magnetic Resonance) using a heat-accumulating phosphor sheet employs a wet system. In a wet system, a reproduction image which has been photographed or recorded on a silver salt photographing photosensitive material is obtained through wet processing.
In contrast, recent efforts have focused on a recording apparatus that employs a dry system rather than a wet process. Such a recording apparatus uses a film of photosensitive and/or thermal-sensitive photothermographic material or thermal-development recording material (hereinafter referred to as photothermographic material). In a dry system recording apparatus, a photothermographic material is irradiated (scanned) with a laser beam to form a latent image in an image exposure section, brought into contact with heating means to undergo thermal development in a thermal development section, and discharged out of the apparatus.
Such a dry system is advantageous in that image formation is completed in a shorter time than in a wet system and that the issue of waste liquid disposal is not involved, and demand for a dry system is expected to increase.
The Japanese applicant has previously filed several applications on thermal development apparatus such as that shown in FIG. 4 (see, for example, JP-A-2003-285455) with Japanese Patent Office.
A thermal development apparatus of the related art will be described hereinafter with reference to FIGS. 4 to 8.
FIG. 4 shows a schematic structural view of a thermal development apparatus 100 having mounted therein an image forming apparatus 1 of the related art. The thermal development apparatus 100 is an apparatus which uses a photothermographic material which does not require a wet photo-development process, and forms a latent image on the photothermographic material by means of scanning exposure with a laser light beam, and thereafter effects thermal development to obtain a visible image, followed by slow cooling and cooling to room temperature.
The basic components of the thermal development apparatus 100 are a photothermographic recording material feed section A, an image exposure section (corresponding to the image forming apparatus 1) B, a thermal development section C, a slow cooling section D, and a cooling section E, in the sequence of a photothermographic material path. The thermal development apparatus 100 is also provided with delivery means located at important points between the sections, which deliver the photothermographic material, and with a power/control section F for driving/controlling each section. The power/control section F is provided with a CPU, whereby various controls (exposure control, running speed control, and others) can be operated.
The thermal development apparatus 100 is arranged such that: the power/control section F is disposed on the bottommost portion thereof; the photothermographic recording material feed section A is disposed on the power/control section F; and the image exposure section B, the thermal development section C, the slow cooling section D, and a cooling section E are disposed on the thermographic material feed section A, wherein the image exposure section B and the thermal development section C are located close to each other.
According to the configuration, the exposure and thermal development processing can be carried out within a short conveyance distance so as to minimize the transport path of the photothermographic material and shorten the required time to output one cut sheet. Furthermore, one cut sheet of the photothermographic material can be subjected to the steps of exposure and thermal development simultaneously.
The photothermographic material to be used may be a photothermographic material or a photo-thermal sensitive recording material. The photothermographic material is a photosensitive material which records (exposes) an image with a light beam (e.g., a laser beam), and the colors thereof are developed by thermal development. Meanwhile, the photo-thermal sensitive recording material is a photosensitive material which records image with a light beam, and the colors thereof are developed by thermal development, or the colors thereof are developed simultaneously with image recording by a heat mode (heat) of the laser beam, followed by color fixation with light radiation.
The photothermographic recording material feed section A is a section in which a photothermographic material is picked up from a supply tray one cut sheet at a time and fed downstream to the image exposure section B, and the feed section A comprises: three loading sections 10a, 10b, and 10c; three feed roller pairs 13a, 13b, and 13c which are provided to the respective feed sections; and a delivery roller and delivery guides, which are not shown. Specifically, inside the loading sections 10a, 10b, and 10c, which are provided in a triple-stacking structure, supply trays 15a, 15b, and 15c are inserted. In the supply trays, photothermographic materials of different sizes (e.g., B4 size, a double-legal size (356 by 432 mm)) are contained so that a size and an orientation of a material can be selected from those contained in respective trays.
The photothermographic material, manufactured in a sheet form, is usually available in the form of a stack of a prescribed number (e.g., 100) of cut sheets, packaged in a bag or with a band. The packages are housed in the respective supply trays and loaded in respective layers of the photothermographic recording material feed section A.
FIG. 5 is a enlarged cross-sectional view of driving rollers, including their vicinity, which convey a photothermographic material 5 supplied from the photothermographic recording material feed section A to the image exposure section B.
A driving roller 21 receives a driving force via transmission means such as gears or belts from an unillustrated driving means such as a motor, thereby rotating clockwise in FIG. 5. A driving roller 22, having the same structure as the driving roller 21, is provided at the boundary between a sloped portion 26 and an abutting section 29, for the purpose of discharging the photothermographic material 5.
An example of the driving roller 21 is described in detail below. The driving roller 21 is disposed so as to oppose a bent portion 31 which is a boundary between the abutting section 29 and a sloped portion 25. As shown in FIG. 5B, which shows a enlarged schematic side view of a portion of FIG. 5A, the driving roller 21 is preferably disposed in the range where a straight line M, which passes through the bent portion 31 (the point where the angle changes) of a guide plate 23 and bisects the inner angle (180°-φ) of the guide plate, contacts the outer periphery of the driving roller 21. Note that no particular limitation is imposed on the relationship between the diameter of the driving roller 21 and the length of the guide plate 23.
A predetermined gap G is formed between the peripheral surface of the driving roller 21 and the guide plate 23. This gap G is preferably equal to 10 times a thickness “t” of the photothermographic material 5 (t≦G≦10t).
In the above structure of a conveying section for the sub-scanning direction 17, when the photothermographic material 3 enters from the leading end of the sloped portion 25, the leading end of the photothermographic material 3 enters into the region between the guide plate 23 and the driving roller 21. In this process, because the abutting section 29 of the guide plate 23 and the sloped portion 25 are bent to form a predetermined angle φ, when the photothermographic material 3 moves from the sloped portion 25 to the abutting section 29, the photothermographic material 3 is flexed. This flexure imparts an elastic repulsion onto the photothermographic material 3 itself. In response to this elastic repulsion, a predetermined frictional force arises between the photothermographic material 3 and the driving roller 21, and the conveying driving force is reliably transmitted from the driving roller 21 to the photothermographic material 3. Consequently, the photothermographic material 3 is conveyed.
The gap G between the driving roller 21 which is driven clockwise and the guide plate 23 is set within the range of t to 10t (t is the thickness of the photothermographic material 3). Therefore, when the photothermographic material 3 enters between the guide plate 23 and the driving roller 21, the conveyance of the photothermographic material 3 is not affected by vibration or the like of the driving roller 21 due to an external disturbance. In other words, when an external disturbance arises, it is absorbed by an elastic force (displacement in the direction of thickness) of the photothermographic material 3 and does not affect conveyance.
With the presence of the sloped portion 26 and the driving roller 22, even at a discharging of the photothermographic material 3 from the guide plate 23, bending of the photothermographic material 3 produces an elastic repulsion, whereby a predetermined frictional force arises between the photothermographic material 3 and the driving roller 22, and the photothermographic material 3 is reliably conveyed.
Also, the photothermographic material 3 is pressed onto the abutting section 29, which suppresses fluttering of the photothermographic material 3 up from the conveying surface. In other words, vertical fluttering is suppressed. When a laser beam is irradiated onto the photothermographic material 3 between the driving rollers, a satisfactory recording free from exposure displacement can be obtained.
The image exposure section B scans the photothermographic material conveyed from the photothermographic recording material feed section A, with a light beam L in the main scanning direction. It also conveys the photothermographic material in the sub-scanning direction (i.e., the conveying direction) perpendicular to the main scan direction, thereby recording a desired image on the photothermographic material to form a latent image.
Next, the image exposure section B will be described.
FIG. 6 shows the image exposure section B, wherein 1 denotes an image forming apparatus of the related art, 2 denotes a semiconductor laser, and 5 denotes a photosensitive material. A light beam 111 emitted from the semiconductor laser 2 is collimated by a collimator lens 112, and subsequently impinges upon a polygon mirror 113, which serves as main scanning means. The light beam 111 is reflected and deflected by the polygon mirror 113 in the direction indicated by arrow A, and subsequently the laser beam 111 passes through a scanning lens 114, which is generally constituted of an fθ lens, and scans the photosensitive material 5 in a main scanning direction, indicated by arrow X. The photosensitive material 5 is conveyed at a predetermined speed by a driving roller 116 serving as sub-scanning means in the direction indicated by arrow Y, which is perpendicular to the main scanning direction X. As described above, the photosensitive material 5 can be scanned by the light beam 111 in the main scanning and sub-scanning directions.
Meanwhile, a digital image signal D is subjected to a gradation correction process in accordance with a gradation correction table in a gradation correction device 120 and fed into a D/A converter 121, wherein the digital image signal D is converted into an analog image signal S. The image signal S is amplified by a variable gain amplifier 122 and is then fed into a third switch 123. The third switch 123 is switched by a control circuit 124, and when the third switch 123 is in a closed position, the image signal S is fed into a semiconductor laser drive circuit 125 as a modulating signal. The semiconductor laser driving circuit 125 drives the semiconductor laser 2, and when the image signal S is fed into the semiconductor laser driving circuit 125, the semiconductor laser 2 is directly modulated in accordance with the image signal S. As described above, the intensity of the light beam 111 is modulated on the basis of the image data D, and the image carried by the image data D is recorded as a photographic latent image on the photosensitive material 5. Thereafter, the photosensitive material 5 is subjected to a thermal development process to obtain a visible image from the latent image.
The semiconductor laser drive circuit 125 is connected to a first driving signal generator 132 via a first switch 130 and to a second driving signal generator 133 via a second switch 131. These signal generators 132 and 133 respectively generate a first fixed-level driving signal S1 and a second fixed-level driving signal S2, which respectively drive the semiconductor laser 2 at predetermined outputs. The switching of the first switch 130 and that of the second switch 131 are controlled by the control circuit 124.
Meanwhile, at a position outside of the effective main scanning region of the light beam 111 with respect to the photosensitive material 5, there is provided a main scanning start point detecting sensor 134, comprising a photodiode for detecting the laser beam 111 or the like. Inside the scanning line, a leading end detecting sensor 135 is provided. The leading end detecting sensor 135 allows the laser beam 111, which is located within the effective main scanning region, to receive a beam. The leading end detecting sensor 135 may comprise a photodiode or the like. Output signals P1 and P2 generated by the main scanning start point detecting sensor 134 and the leading end detecting sensor 135, respectively, are input to the control circuit 124.
When the photosensitive material 5 is conveyed by the driving roller 116 in the direction indicated by the arrow Y and the leading end of the photosensitive material 5 reaches the position indicated by the arrow B, the control circuit 124 detects this state by means of, for example, predetermined sequence control. Upon this detection, the control circuit 124 starts controlling the opening and closing operations of the first switch 130 and the second switch 131. Specifically, during the main scanning period, in which the light beam 111 impinges upon the vicinity of the main-scanning start point detecting sensor 134, the first switch 130 is set to a close position, and the second switch 131 is set to an open position. During the effective main scanning period, in which the light beam 111 is capable of scanning the photosensitive material 5, the first switch 130 is set to the open position, and the second switch 131 is set to the close position.
During the main scanning period, in which the light beam 111 impinges upon the vicinity of the main-scanning start point detection sensor 134, the first fixed-level driving signal S1 is input to the semiconductor laser driving circuit 125. The semiconductor laser 2 is thereby caused to emit the light beam 111 with a first predetermined intensity level L1.
Also, during the effective main scanning period, the second fixed-level driving signal S2 is input to the semiconductor laser driving circuit 125, and the semiconductor laser 2 is thereby caused to emit the light beam 111 with a second predetermined intensity level L2.
In addition, controlling the opening and closing operations of the first switch 130 and the second switch 131 in a manner approximately synchronized with the main scanning of the light beam 111 can be achieved by having the polygon mirror drive circuit 113 input a polygon mirror rotation angle signal R to the control circuit 124, or by other means.
When the light beam 111 from the semiconductor laser 2 is received, the main-scanning start point detection sensor 134 generates the output signal P1. The leading end detection sensor 135 generates the output signal P2, such as that shown in FIG. 6. During the main scanning period, in which the light beam 111 impinges upon the vicinity of the main-scanning start point detection sensor 134, the intensity of the light beam 111 is set at the first level L1, which is comparatively high. Therefore, the output signal P1 produced by the main-scanning start point detection sensor 134 upon detection of the light beam 111 rises with a clear waveform. Accordingly, in the control circuit 124, a horizontal synchronizing signal Hsync, which indicates that the light beam 111 has passed through the predetermined main-scanning start point, can be generated by, for example, shaping the waveform of the output signal P1.
When the photosensitive material 5 is further conveyed and its leading end reaches the position exposed to the light beam 111, the light beam 111, which has been set to enter the leading end detection sensor 135, is blocked by the leading end of the photosensitive material 5. As a result, a pulsed waveform, which has been generated as a result of the light beam detection, disappears from the output signal P2 of the leading end detection sensor 135. The control circuit 124 detects the disappearance of the pulsed waveform. Thereafter, during the effective main scanning period in which the second switch 131 has been closed, the control circuit 124 opens the second switch 131 and closes the third switch 123. During the effective main scanning period, the image signal S is input to the semiconductor laser driving circuit 125, and the semiconductor laser 2 emits the light beam 111 which has been modulated in accordance with the image signal S, thereby subjecting the photosensitive material 5 to image recording.
In this case, the input timing of the image signal S to the semiconductor laser driving circuit 125 is synchronized with the main scanning of the light beam 111, by means of inputting a pixel clock signal synchronized with a horizontal sync signal Hsync produced by the control circuit 124 in accordance with the signal P1 output from the main-scanning start point detection sensor 134 is inputted to a digital-to-analog converter 121, to thus control a timing at which the digital image data D are to be subjected to digital-to-analog conversion.
As described above, when the photosensitive material 5 conveyed in the direction indicated by the arrow Y reaches a position where the leading end thereof is exposed to the light beam 111, the light beam 111, which has been set to enter the leading end detection sensor 135, is blocked by the leading end of the photosensitive material 5. As a result, the pulsed waveform, which has been generated in response to the laser beam detection, disappears. In this process, because the permeability of the photosensitive material 5 is lowered by addition of sensitized material, the light beam 111 can be reliably blocked.
The thermal development section C effects thermal development by means of performing thermal treatment of the post-scan photothermographic material 5 while conveying the same. The thermal development section C has such a structure that a plurality of plate heaters 51a, 51b, and 51c, which are arranged in series in the conveying direction of the photothermographic material and serve as a heating member with a required heating capability for processing the photothermographic material 5, are curved and are arranged so as to form a serial circular arc.
More specifically, the thermal development section C including the plate heaters 51a, 51b, and 51c has a structure that, as shown in FIG. 4, each plate heater is provided with a concave surface, causing the photothermographic material 5 to come in contact with the concave surface of the plate heater and sliding the photothermographic material in relation to the plate heaters. As conveying means of the photothermographic material 5, there are provided a feeding roller 53 and a plurality of pressing rollers 55, which also serve to transfer heat from each plate heater to the thermal development recording material. The pressing rollers 55 are in contact with the peripheral surface of a rotating disk 52, and are driven by the rotation of the rotating disk 52. As the press rollers 55, metal rollers, resin rollers, rubber rollers, or the like can be used. According to the configuration described above, the photothermographic material 5 is pressed against the plate heaters 51a, 5b, and 51c while being conveyed. Consequently, buckling of the photothermographic material 5 can be prevented. At the downstream end of the photothermographic material 5 path inside the thermal development section C, there is provided a discharge roller 57 for transferring the photothermographic material.
FIG. 7 is an explanatory diagram showing the layer constitution of a photothermographic material.
First, the constitution of the photothermographic material 5 will be described. As shown in FIG. 7, the photothermographic material is formed by means of: coating a base film—which has a thickness of 176 μm and is composed of PET (polyethylene terephthalate) or other material—with an emulsion layer Em having a thickness of 20 μm; and by further coating the emulsion layer Em with a protective layer PC having a thickness of 4 μm. On the back side of the base film, a backcoat layer BC and an antihalation layer AH, having a total thickness of 3 μm, are coated. The total thickness of the photothermographic material 5 is set within the range of 150 to 250 μm.
The refractive indexes of the respective layers are set as follows: 1.52 for the protective layer PC, 1.54 for the emulsion layer Em, 1.66 for the base film (PET), 1.52 for the backcoat layer BC, 1.52 for the antihalation layer AH, for an average of approximately 1.5 to 1.7. A blank photothermographic material 5 having an optical permeability of 50% or lower is used, with an optical permeability of 30% or lower being preferred.
When a laser beam is radiated from the protective layer PC side of the photothermographic material 5, the laser beam travels ahead while its light path is refracted, and reaches the interface of the bottommost backcoat layer BC and the air below the antihalation layer AH. The laser beam is reflected at the interface, and the reflected beam returns back to the protective layer PC. When the distance Lm between the laser beam incoming position P1 and the outgoing position P2 of the reflected beam on the surface of the photothermographic material is larger than a diameter of the laser beam, the problem of interference can be avoided.
FIG. 8 is an enlarged perspective view of one of the plate heaters 51a, 51b, and 51c; for example, the plate heater 51b. The drawing shows the heater rack with its cover removed. The plate heater 51b includes an aluminum guide plate 51G, a silicon rubber heater 51H, a thermistor (not shown), a heater terminal (protector) 51P, and pressing rollers 55.
The aluminum guide plate 51G is shaped to form a concave surface along the conveying direction of the photothermographic material. In the width direction of the aluminum guide plate 51G, seven pressing rollers 55 are laid at uniform intervals along the conveying direction. The metal pressing rollers 55 act to convey a photothermographic material, which has been transferred on the concave surface, while pressing it against the concave surface.
The curved plate heater above is an embodiment and may be built to include an endless belt and a separation pawl through use of another flat plate heater or a heating drum.
The photothermographic material 5 conveyed out from the thermal development section C is gradually cooled carefully so as not to generate any wrinkle and to have a curled shape at the slow cooling section D.
Within the slow cooling section D, a plurality of slow cooling roller pairs 59 are arranged so as to impart a desirable constant curvature R in the path of the photothermographic material 5. This implies that the photothermographic material 5 is delivered with the constant curvature R until it is cooled to or below the glass transition point of the material. Because the curvature is intentionally imparted to the photothermographic material, no unnecessary curl is formed before the photothermographic material is cooled to or below the glass transition point. No new curl is formed at the grass transition point or less; therefore, a curl amount is not varied.
Furthermore, the temperatures of the slow cooling rollers themselves and the internal atmosphere of the slow cooling section D are regulated. Such temperature regulation minimizes the difference between the condition immediately after startup and that after sufficient running. Thereby, the density variation can be reduced.
The photothermographic material 5, which is cooled to or below the glass transition point of the material in the slow cooling section D, is conveyed to the cooling section E by the rollers pair 59 provided in the vicinity of the exit of the slow cooling section D.
In the cooling section E, a cooling plate 61 is provided. Here, the photothermographic material 5 is further cooled to a temperature at which an operator does not receive a burn when touching it. Thereafter, the photothermographic material is discharged to a discharge tray 16 by a discharge roller pair 63.